1. Field of Invention
This invention is in the field of bistatic radars using space time adaptive processing where transmit pulse coding minimizes the effect of Range/Doppler ambiguities.
2. Description of the Related Art
Space Time Adaptive Processing (STAP) is generally used in Air Moving Target Indicators (AMTI) and Ground Moving Target indicators (GMTI) radar applications to cancel the stationary ground clutter and/or strong scatterers thus increasing probability of detection of moving targets. In a AMTI/GMTI monostatic radar, a map is created of a frequency change (Doppler) and range from the radar returns. The co-location of receiver and transmitter in a monostatic radar facilitates the collection of pulse Doppler data and creation of constant range and constant Doppler contours as only the motion of one receiving/transmitting platform needs to be accounted for.
Conversely, in a bistatic radar there is a separation between the transmitter portion (illuminator) and the receiver. The receiver and transmitter are on their own respective platforms having separate, un-correlated motions. I spite of these separate motions, GMTI and AMTI are computed from accurate phase information to facilitate deriving a phase coherent image at the receiver. Thus, a challenge in the design and operation of bistatic radars is to maintain phase coherency between the transmitter (illuminator) and the receiver, especially when used as GMTI and AMTI for moving targets against stationary clutter and a strong scatterer (or jammer).
Further, a bistatic radar, because of the spacial separation between the transmitter (illuminator) and the receiver, is faced with the problem of range/Doppler ambiguity. Although the receiver and transmitter have separate motion components, accurate return phase and timing information needs to be preserved to re-constitute a phase coherent, range accurate image at the receiver. Similarly, the ambiguity problem also increases in the Doppler plane further posing a challenge to AMTI and, GMTI operation.